Electrical resistor



1967 F. P. SANDONE, JR., ETAL 3,319,210

ELECTRICAL RESISTOR Filed April 10, 1964 lNVE/VTO/PS. FRANK P. $A/VO0N'.JR. WILL/AM L. SHIV/WELD ATTORNEY Has 7 j 42 United States Patent 3,319,210 ELECTRICAL RESISTOR Frank P. Sandone, Jr., Secane, and William V. Stanfield, Huntingdon Valley, Pa., assignors to IRC, Inc. Filed Apr. 10, 1964, Ser. No. 358,849 Claims. (Cl. 338-322) The present invention relates to an electrical resistor and the method of making the same. More particularly, the present invention relates to a termination for a wire wound resistor and the method of making the same.

In general, wire wound electrical resistors comprise a fine resistance wire helically wound around and along a core of an electrical insulating material, a terminal secured to each end of the winding, and a protective casing surrounding the winding with the terminals projecting from the casing. One type of terminal used for such wire wound resistors, particularly resistors small in size, is a relatively heavy wire of an electrically conductive metal. Such wire terminals must be attached to the resistance winding with both a good mechanical connection and a good electrical connection. A poor electrical connection between the terminal wires and the resistance winding can adversely affect the electrical characteristics of the resistor by altering its resistance value, increasing its noise level, and creating hot spots which can damage the resistance winding. The manner of connecting the terminal Wires to the resistance winding must not only provide a good mechanical and electrical connection therebetween, but also must be capable of being carried out easily and quickly to permit the mass production of the resistors economically.

It is an object of the present invention to provide a novel wire wound electrical resistor.

It is another object of the present invention to provide a novel termination for a wire wound resistor.

It is still another object of the present invention to provide a termination for a wire wound resistor in which a terminal wire is joined to a resistance wire winding with a good mechanical and electrical connection.

It is a further object of the present invention to pro vide a method of connecting a terminal wire to a re sistance wire winding.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a perspective view, partially broken away, of the wire wound resistor of the present invention.

FIGURE 2 is an exploded perspective view of the wire wound resistor of the present invention prior to being assembled.

FIGURE 3 is a longitudinal sectional view of the wire wound resistor of the present invention.

FIGURE 4 is a sectional view taken along line 4-4 of FIGURE 3.

FIGURE 5 is an enlarged sectional view of one end of the resistor of the present invention.

Referring initially to FIGURES 1 and 3 of the drawing, the resistor of the present invention is generally designated as 10.

Resistor comprises a core 12 of an electrical insulating material having a fine resistance wire 14 helically wound therearound along the entire length thereof. A separate electrically conducting metal terminal 16 is secured to each end of the core 12 and the resistance wire winding 14. A casing 18 of an electrical insulating plastic surrounds the core 12, resistance wire winding 14 and portions of the terminals 16.

Core 12 is circular in transverse cross-section, and of a length greater than its diameter. The core 12 may be of any of the well known plastics or may be a cord of natural or synthetic fibers. The resistance wire 14 may be of any of the well known resistance metals or alloys having the desired resistivity and temperature coefiicient of resistance. In making the resistor 10, the resistance wire 14 can be continuously wound around and along a continuous length core 12 which is then cut into shorter pieces of the desired length.

Each of the terminals 16 is of an electrically conductive metal, such as copper, and comprises a terminal wire 20 and a cup-shaped cap 22 secured to one end of the wire 20. As shown in FIGURE 5, the cap 22 is formed as an integral part of the terminal wire 20. However, the terminal wire 20 and cap 22 can be formed separately with the terminal wire welded or riveted to the bottom of the cap.

The terminals 16 are provided on the resistor 10 by inserting each end of the wire wound core into a separate one of the terminal caps 22 so that each cap surrounds a plurality of turns of the wire 14 at the respective end of the core 12. The end portion 22a of each of the terminal caps 22 is crimped around the core 12 and the wire 14 by a suitable tool which applies radially inward pressure to substantially the entire surface of the cap. At the same time that the pressure is applied tothe cap, the cap is heated to a temperature sufi'icient to cause the metal of the cap end portion 22a to flow. The particular temperature to which the cap is heated depends on the melting temperature of the particular metal of the cap. As shown in FIGURE 5, this application of heat and pressure to the cap end portion 22a causes the cap end por-, tion to flow between and around the encompased turns of the wire 14 so that the cap end portion surrounds and intimately engages approximately of the surface of each turn of the wire. In addition, the heat and pressure applied to the cap end portion 22a can cause some fusion between the cap and the turns of the wire 14. The amount of such fusion depends on the particular metals of the cap and the wire.

Although various tools can be used to crimp the cap 22 around the core 12 and resistance wire 14, in general, such a tool comprises a pair of dies having aligned, mating, semi-cylindrical grooves in their opposed surfaces. The dies may be heated electrically. Thus, when the dies are brought together around the cap end portion 22a, they apply the necessary heat and pressure to the cap. During the crimping operation, the excess metal of the cap flows radially outwardly between the opposed surface of the dies forming the flanges 22b 0n the cap.

By having the metal of the caps 22 extending between the turns of the wire 14 there is provided a strong mechanical connection between the terminals 16 and the wire wound core. The intimate engagement between the caps 22 and wire 14 provides a good electrical connection between the terminals 16 and the wire 14. The resistor 10 of the present invention has been found to have better characteristics than those of a similar resistor in which the caps were crimped onto the wire wound core only by pressure and without the application of heat. The following table shows the magnitude of the improvement in the characteristics of the resistor 10 of the present invention over the characteristics of a similar resistor in which the terminal caps were crimped onto the wire wound core only by pressure.

The improvements shown in the above table were obtained by comparing the results of testing two groups of resistors of substantially identical size and construction except that the resistors of one of the groups were made in accordance with the present invention, the caps of the terminals were crimped onto the wire wound core under heat and pressure, and the resistors of the other group were made by crimping the caps of the terminals onto the wire wound core only by the application of pressure. The resistors of each group were individually tested and the average of the test results of each group was compared to obtain the magnitude of the improvement of the resistor of the present invention shown in the table. The tests carried out are the standard tests used in the resistor industry to determine the characteristics of a resistor. Except for the pull strength test, the results of each of the tests reflect a change in resistance of the resistor caused by the test. The pull strength test was carried out on the resistors prior to applying the insulating casing 18 to the resistors to determine the mechanical bond between the terminals and the wire wound core.

As can be seen from the above table, the resistor of the present invention underwent a much smaller change in resistance during the tests than the similar resistor having a terminal cap which was crimped onto the resistor only under pressure. Thus, the resistor of the present invention having a terminal cap crimped thereon under heat and pressure is more stable electrically than the same resistor having the terminal cap crimped thereon only under pressure. Also, the pull strength test shows that the method of the present invention provides a stronger mechanical connection between the terminal and the wire wound core.

Although the terminals 16 are shown as comprising a cup-shaped cap to which the terminal wire is attached, the terminal can also comprise a metal strip wrapped around or partially around the end of the wire Wound core and crimped thereto under heat and pressure in accordance with the method of the present invention. The terminal wires would then be attached to the metal strip.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

We claim:

1. An electrical resistor comprising a core of electrical insulating material, a resistance wire helically wound around the core along thefull length of the core, and a separate metal terminal extending around each end of the core and some of the turns of the resistance wire, each of said terminals being crimped around the core and the encompassed turns of the resistance wire by the application of heat and pressure with the metal of the terminal extending into the spaces between the encompassed turns of the resistance wire along the entire length of said spaces, and directly and intimately engaging the surface of the encompassed turn of the resistance wire.

2. An electrical resistor in accordance with claim 1 in which each of the terminals comprises a metal strip wrapped around the core and a plurality of turns of the of the resistance wire.

3. An electrical resistor in accordance with claim 1 in which each of the terminals comprises a cup-shaped metal cap fitting over each end of the core and surrounding a plurality of turns of the resistance wire.

4. An electrical resistor in accordance with claim 3 in which each of the caps is crimped around the core and wire substantially around the entire periphery of the cap.

5. An electrical device in accordance with claim 1 in which the terminal is fused directly to the encompassed turns of the wire.

References Cited by the Examiner UNITED STATES PATENTS 1,908,859 5/1933 ONeill 17494 X 2,035,911 3/1936 Mucher 338-332 X 2,371,469 3/1945 Rogoif 339-476 2,535,808 12/1950 Mucher 338-275 X 2,838,639 6/1958 Planer et al. 338-218 X 2,938,069 5/1960 Toedtman et al. 339-276 X 2,977,561 3/1961 Pugh et a1 338-237 2,983,779 5/1961 Dumiere et al. 339l77 X 2,987,813 5/1961 Pope et al 29--471.l 3,074,150 1/1963 Berg 339-276 X 3,212,044 10/1965 Cloud 338-66 3,229,237 1/ 1966 Berkelhamer 338266 3,231,964 2/1966 Bennett 17.990 X ANTHONY BARTIS, Primary Examiner.

, RICHARD M. WOOD, Examiner.

V. Y, MAYEWSKY, Assistant Examiner. 

1. AN ELECTRICAL RESISTOR COMPRISING A CORE OF ELECTRICAL INSULATING MATERIAL, A RESISTANCE WIRE HELICALLY WOUND AROUND THE CORE ALONG THE FULL LENGTH OF THE CORE, AND A SEPARATE METAL TERMINAL EXTENDING AROUND EACH END OF THE CORE AND SOME OF THE TURNS OF THE RESISTANCE WIRE, EACH OF SAID TERMINALS BEING CRIMPED AROUND THE CORE AND THE ENCOMPASSED TURNS OF THE RESISTANCE WIRE BY THE APPLICATION OF HEAT AND PRESSURE WITH THE METAL OF THE TERMINAL EXTENDING INTO THE SPACES BETWEEN THE ENCOMPASSED TURNS OF THE RESISTANCE WIRE ALONG THE ENTIRE LENGTH OF SAID SPACES, AND DIRECTLY AND INTIMATELY ENGAGING THE SURFACE OF THE ENCOMPASSED TURN OF THE RESISTANCE WIRE. 